Relative importance of tree species richness, tree functional type, and microenvironment for soil macrofauna communities in European forests.

Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications.

Spinosad application in an apple orchard affects both the abundance of the spider Araneus diadematus and its web construction behaviour.

The principles of organic production are based on the respect of ecological processes including the promotion of natural enemies to control pests. However, as a last resort, some natural pesticides can be applied such as the pesticide spinosad. This neurotoxic insecticide is now widely used even in non-organic production systems. As generalist predators, spiders, and especially orb web spiders, which prey on flying pests, are thought to be useful for biocontrol. To study the effects of spinosad on orb web spiders, we applied spinosad (Success4®) at the normal application rate (96 g ha-1) in an orchard covered by nets where Araneus diadematus was very abundant. Its abundance (number of webs), location when present on the web and web characteristics were determined one day before (D - 1) and 1, 3, 6, 10 and 14 days after the application (D + 1, D + 3, D + 6, D + 10 and D + 14). After spinosad application, at D + 1 and D + 14, the number of A. diadematus webs decreased by 28% and 47%, respectively, compared to D - 1 where we observed on average 0.2 webs m-2. This decrease is likely due to a combination of direct pesticide effects, reduced prey availability and mechanical effects of the air blast sprayer. The short-term toxicity of spinosad was assessed using behavioural markers: (i) the percentage of abnormally located spiders (i.e. neither in the centre of the web nor hidden under the apple leaves) for 30 and 50% of the webs at D + 1 and D + 3 respectively, (ii) the percentage of incomplete webs (made only of the non-sticky spiral) in 35 and 75% of the cases at D + 1 and D + 3 respectively and (iii) one web characteristic, the mean parallelism between spirals, that was significantly reduced at D + 1 compared to D - 1. The study of the other web characteristics indicated that spiders did not modify the capture area but rather significantly decreased their investment in silk at D + 6 and D + 10 by reducing the number of radii and spiral turns. Overall, the application of spinosad (Success4®), representing a triple disturbance (mechanical, toxicological and alimentary), has a negative impact on the orb web spider A. diadematus and should thus be used with caution if growers want to promote the contribution of these spiders to natural biocontrol in their fields.

The onset of piscivory in a freshwater fish species: analysis of behavioural and physiological traits.

The onset of piscivory in fish, resulting in a shift from zooplankton or invertebrate to fish prey, was studied on pikeperch (Sander lucioperca) larvae displaying and not displaying piscivorous behaviour at different ages (23, 30, 37, 44 and 52 days post-hatching) using behavioural (attack, capture and swimming activity), morphological (allometry) and digestive enzymatic (trypsin, α-amylase and pepsin) analyses. The shift from zooplanktonic food items (Artemia nauplii) to a piscivorous diet did not occur at the same time for all individuals within the same cohort. Predation tests, conducted under controlled conditions (20°C; ad libitum feeding), showed that some larvae attacked fish prey as early as the age of 3 weeks [11.0 ± 1.3 mm total length (TL)], whereas others did not start until the age of 6 weeks (16.6 ± 1.9 mm TL). Piscivorous individuals were bigger, with larger heads, longer tails, higher acid protease and lower alkaline protease activities, than non-piscivorous conspecifics. In conclusion, high interindividual variability in morphological and digestive system developments linked to the development of predatory abilities could induce cannibalism in fish.

The impact of management strategies in apple orchards on the structural and functional diversity of epigeal spiders.

Apple orchards are agro-ecosystems managed with high levels of inputs and especially pesticides. Epigeal spider communities were sampled in three seasons using pitfall traps in 19 apple orchards with four different management strategies (abandoned, under organic, Integrated Pest Management or conventional protection) and thus significantly different pesticide usage. The abundance and diversity of the spider communities was the highest in abandoned orchards. Higher diversity and evenness values were the only difference in spider communities from the organic orchards compared to the other commercial orchards. The analysis of five ecological traits (proportion of aeronauts, type of diet, overwintering stages, body size and maternal care), however, clearly showed differences in the spiders from the organic orchards. The spider species in the other commercial orchards were smaller and have higher dispersal abilities. Seven bioindicator species were identified in abandoned orchards, two species in organic ones (only Lycosidae) and one species in conventional orchards (Linyphiidae).

Finding the Best Match: A Ranking Procedure of Fish Species Combinations for Polyculture Development.

Polyculture is a potentially interesting rearing practice for future aquaculture developments. Nevertheless, it may result in beneficial as well as detrimental consequences for fish production. One way to maximize the benefits of polyculture is to combine species with high levels of compatibility and complementarity. This requires the development of a ranking procedure, based on a multi-trait assessment, that highlights the most suitable species combinations for polyculture. Moreover, in order to ensure the relevance of such a procedure, it is important to integrate the socio-economic expectations by assigning relative weights to each trait according to the stakeholder priorities. Here, we proposed a ranking procedure of candidate fish polycultures (i.e., species combinations that could be potentially interesting for aquaculture) based on a multi-trait assessment approach and the stakeholder priorities. This procedure aims at successively (i) weighting evaluation results obtained for each candidate polyculture according to stakeholder priorities; (ii) assessing differentiation between candidate species combinations based on these weighted results; and (iii) ranking differentiated candidate polycultures. We applied our procedure on three test cases of fish polycultures in recirculated aquaculture systems. These test cases each focused on a target species (two on Sander lucioperca and one on Carassius auratus), which were reared in two or three different alternative candidate fish polycultures. For each test case, our procedure aimed at ranking alternative combinations according to their benefits for production and/or welfare of the target species. These benefits were evaluated based on survival rate as well as morphology, behavioral, and physiological traits. Three scenarios of stakeholder priorities were considered for weighting evaluation results: placing a premium on production, welfare, or both for the target species. A comparison of our procedure results between these scenarios showed that the ranking changed for candidate polycultures in two test cases. This highlights the need to carefully consider stakeholder priorities when choosing fish polycultures.

AquaDesign: A tool to assist aquaculture production design based on abiotic requirements of animal species.

Farming new species and promoting polyculture can enhance aquaculture sustainability. This implies to define the rearing conditions that meet the ecological requirements of a target species and/or to assess if different species can live in the same farming environment. However, there is a large number of rearing conditions and/or taxon combinations that can be considered. In order to minimise cumbersome and expensive empirical trials to explore all possibilities, we introduce a tool, AquaDesign. It is based on a R-script and package which help to determine farming conditions that are most likely suitable for species through in silico assessment. We estimate farming conditions potentially suitable for an aquatic organism by considering the species niche. We define the species n-dimensional niche hypervolume using a correlative approach in which the species niche is estimated by relating distribution data to environmental conditions. Required input datasets are mined from several public databases. The assistant tool allows users to highlight (i) abiotic conditions that are most likely suitable for species and (ii) combinations of species potentially able to live in the same abiotic environment. Moreover, it offers the possibility to assess if a particular set of abiotic conditions or a given farming location is potentially suitable for the monoculture or the polyculture of species of interest. Our tool provides useful pieces of information to develop freshwater aquacultures. Using the large amount of biogeographic and abiotic information available in public databases allows us to propose a pragmatic and operational tool even for species for which abiotic requirements are poorly or not available in literature such as currently non-produced species. Overall, we argue that the assistant tool can act as a stepping stone to promote new aquatic productions which are required to enhance aquaculture sustainability.

Loss of legs: is it or not a handicap for an orb-weaving spider?

Leg loss is a common phenomenon in spiders, and according to the species 5% to 40% of the adults can present at least one missing leg. There is no possibility of regeneration after adult moult and the animal must manage with its missing appendages until its death. With the loss of one or more legs, female orb-weaving spiders can be penalized twice: firstly, because the legs are necessary for web construction and secondly, the legs are essential for the control of the prey after its interception by the web. During development, spiders may be also penalized because regeneration has energetic costs that take away resources for survival, growth and reproduction. All these consequences should influence negatively the development of the spider and thus its fitness. We investigated the impact of leg loss in the orb-weaving spider, Zygiella x-notata by studying its frequency in a natural population and web building and prey capture behaviours in laboratory. In field populations, 9.5% to 13%, of the adult females presented the loss of one or more legs; the majority of individuals had lost only one leg (in 48% of cases, a first one). Leg loss seems to affect all the adult spiders, as there is no difference of mass between intact spiders and those with missing leg. Data obtained with laboratory-reared spiders, showed that the loss of legs due to the moult is rare (less than 1%). Considering changes in web design, spiders with missing legs decreased their silk investment, increased the distance between spiral turns but did not change the capture surface of the web. Under our laboratory experimental conditions, spiders with one or two lost legs did not present any difference in prey capture efficiency. In laboratory conditions, spiders with lost leg(s) did not show any difference in egg sac production or in longevity (adult lifespan) compared to intact spiders.

When more is more: taking advantage of species diversity to move towards sustainable aquaculture.

Human population growth has increased demand for food products, which is expected to double in coming decades. Until recently, this demand has been met by expanding agricultural area and intensifying agrochemical-based monoculture of a few species. However, this development pathway has been criticised due to its negative impacts on the environment and other human activities. Therefore, new production practices are needed to meet human food requirements sustainably in the future. Herein, we assert that polyculture practices can ensure the transition of aquaculture towards sustainable development. We review traditional and recent polyculture practices (ponds, recirculated aquaculture systems, integrated multi-trophic aquaculture, aquaponics, integrated agriculture-aquaculture) to highlight how they improve aquaculture through the coexistence and interactions of species. This overview highlights the importance of species compatibility (i.e. species that can live in the same farming environment without detrimental interactions) and complementarity (i.e. complementary use of available resources and/or commensalism/mutualism) to achieve efficient and ethical aquaculture. Overall, polyculture combines aspects of productivity, environmental protection, resource sharing, and animal welfare. However, several challenges must be addressed to facilitate polyculture development across the world. We developed a four-step conceptual framework for designing innovative polyculture systems. This framework highlights the importance of (i) using prospective approaches to consider which species to combine, (ii) performing integrated assessment of rearing environments to determine in which farming system a particular combination of species is the most relevant, (iii) developing new tools and strategies to facilitate polyculture system management, and (iv) implementing polyculture innovation for relevant stakeholders involved in aquaculture transitions.

Comparison of single- and multi-trait approaches to identify best wild candidates for aquaculture shows that the simple way fails.

In agriculture, diversifying production implies picking up, in the wild biodiversity, species or populations that can be domesticated and fruitfully produced. Two alternative approaches are available to highlight wild candidate(s) with high suitability for aquaculture: the single-trait (i.e. considering a single phenotypic trait and, thus, a single biological function) and multi-trait (i.e. considering multiple phenotypic traits involved in several biological functions) approaches. Although the former is the traditional and the simplest method, the latter could be theoretically more efficient. However, an explicit comparison of advantages and pitfalls between these approaches is lacking to date in aquaculture. Here, we compared the two approaches to identify best candidate(s) between four wild allopatric populations of Perca fluviatilis in standardised aquaculture conditions. Our results showed that the single-trait approach can (1) miss key divergences between populations and (2) highlight different best candidate(s) depending on the trait considered. In contrast, the multi-trait approach allowed identifying the population with the highest domestication potential thanks to several congruent lines of evidence. Nevertheless, such an integrative assessment is achieved with a far more time-consuming and expensive study. Therefore, improvements and rationalisations will be needed to make the multi-trait approach a promising way in the aquaculture development.

TOFF, a database of traits of fish to promote advances in fish aquaculture.

Functional traits can be valuable pieces of information for aquaculture research and management. Although fish traits have been the focus of an abundant research, trait datasets for these organisms are difficult to access and often unpractical to achieve meta-analyses without a time-consuming extensive review. Already available large-scale compilations include trait information for many fish species but not as detailed as required for aquaculture purpose. Here, we introduce the TOFF (i.e. Traits OF Fish), a database focusing on fish functional traits that aims at bringing together behavioral, morphological, phenological, and physiological traits always coupled to environmental measurement context into a single open-source access repository. TOFF hosts data from published field and experimental studies. Here, we release data for 228 traits for 174 species extracted from 165 publications and present a collaborative platform. We ultimately aim at providing an inclusive and accessible data resource to facilitate advances in aquaculture development.

Influence of aging on brain and web characteristics of an orb web spider.

In animals, it is known that age affects the abilities of the brain. In spiders, we showed that aging affects web characteristics due to behavioral alterations during web building. In this study, we investigated the effects of age on the associations between morphological changes to the spider brain and changes in web characteristics. The orb web spider Zygiella x-notata (Araneae, Araneidae) was used to test these relationships. Experiments were conducted on young (19 ± 2 days after adult molt, N = 13) and old (146 ± 32 days, N = 20) virgin females. The brain volume decreased with age (by 10%). Age also had an impact on the number of anomalies in the capture area generated during web building. The statistical relationships between the volume of the brain and web characteristics showed that there was an effect of age on both. Our results showed that in spiders, aging affects the brain volume and correlates with characteristics (anomalies) of the web. As web building is the result of complex behavioral processes, we suggest that aging affects spider behavior by causing some brain alterations.

Temperature modifies activity, inter-individual relationships and group structure in a fish.

A host of abiotic factors modify fish social behavior. However, few studies have characterized the effects of temperature on behavior. In this study, brown trout Salmo trutta fry were reared at 5 different temperatures (4°C, 6°C, 8°C, 10°C, and 12°C). In order to characterize group structure, 3 behavioral parameters were investigated: group social structure (based on inter-individual distances), inter-individual relationships (based on physical contacts), and individual activity. These behavioral parameters were studied at the emergence stage, which corresponds to a switch from a social gregarious life in the gravel to a solitary one in the water column. Data analysis showed that the inter-individual distances increased with increasing temperature, particularly the nearest neighbor distance. The mean number of physical contacts between fry increased at both low and high temperatures. At high temperatures, most fry moved apart from each other after a physical contact. Swimming activity decreased at both the lower and upper temperatures (18% of activity at 4°C, 38% at 8°C, and 12% at 12°C). This study showed that temperature modifies brown trout fry activity, inter-individual relationships, and social behavior, which all affect group cohesion before emergence and can influence their survival and dispersal.

Strong Effects of Temperature on the Early Life Stages of a Cold Stenothermal Fish Species, Brown Trout (Salmo trutta L.).

Temperature is the main abiotic factor that influences the life cycle of poikilotherms. The present study investigated the thermal tolerance and phenotypic plasticity of several parameters (development time, morphometric measures, bioenergetics) for both embryos and fry of a cold stenothermal fish species, brown trout (Salmo trutta L.) in order to allow for a holistic evaluation of the potential effects of temperature. Five temperatures (4°C, 6°C, 8°C, 10°C, and 12°C) were tested, and the effects of temperature were analyzed at three stages: hatching, emergence, and first food intake. A mean of 5,440 (S.E. ± 573) eggs, coming from seven females and seven males (seven families) captured close to Linkebeek (Belgium), were used for each temperature. Maximum survival of well-formed fry at first food intake and better use of energy budget were found at 6°C and 8°C, temperatures at which the possible contribution to the next generation should therefore be greatest. At 12°C, the experimental population fell dramatically (0.9% survival rate for well-formed fry at first food intake), and fry had almost no yolk sac at first food intake. The present results on survival at 12°C are in accordance with predictions of a sharp decrease in brown trout numbers in France over the coming decades according to climate change projections (1°C to 5°C temperature rise by 2100 for France). At 10°C, there was also a lower survival rate (55.4% at first food intake). At 4°C, the survival rate was high (76.4% at first food intake), but the deformity rate was much higher (22% at first food intake) than at 6°C, 8°C, and 10°C. The energetic budget showed that at the two extreme temperatures (4°C and 12°C) there was less energy left in the yolk sac at first food intake, suggesting a limited ability to survive starvation.

Time till death affects spider mobility and web-building behavior during web construction in an orb-web spider.

It is well known that age influences organism mobility. This was demonstrated in vertebrates (such as mammals and birds) but has been less studied in invertebrates with the exception of Drosophila and the nematode Caenorhabditis elegans. Here we studied the influence of age on the mobility of the orb-weaving spider Zygiella x-notata during web construction. The orb-web is a good model because it has a characteristic geometrical structure and video tracking can be used to easily follow the spider's movements during web building. We investigated the influence of age (specifically chronological age, life span, and time till death) on different parameters of spider mobility during the construction of the capture spiral (distance traveled, duration of construction, spider velocity, spider movement, and spider inactivity) with a generalized linear model (GLM) procedure adjusted for the spider mass. The results showed that neither chronological age, nor life span affected the mobility parameters. However, when the time till death decreased, there was a decrease in the distance traveled, the duration of the construction of the capture spiral, and the spider movement. The spider velocity and the time of inactivity were not affected. These results could be correlated with a decrease in the length of the silky thread deposited for the construction of the capture spiral. Spiders with a shorter time till death built smaller web using less silk. Thus, our study suggests strongly that time till death affects spider mobility during web construction but not the chronological age and thus may be a good indicator of senescence.

Web-building management in an orb-weaving spider, Zygiella x-notata: influence of prey and conspecifics.

According to optimal foraging theory, spiders should adapt their web building to environmental variations. Until now, there was no data on the influence of simultaneous information coming from different environmental factors on web building behaviour. Under laboratory conditions, we studied the behaviour of Zygiella x-notata in the presence of prey, conspecifics, or both simultaneously. There was a stimulating effect of prey, but web building was not affected by the presence of conspecifics. When spiders and prey were present simultaneously, the effect was similar to that of prey alone; it seemed that there was no interactive influence of both factors. We discussed about the use of environmental information by spiders in foraging behaviour.

A thesaurus for soil invertebrate trait-based approaches.

Soil invertebrates are known to be much involved in soil behaviour and therefore in the provision of ecosystem services. Functional trait-based approaches are methodologies which can be used to understand soil invertebrates' responses to their environment. They (i) improve the predictions and (ii) are less dependent on space and time. The way traits have been used recently has led to misunderstandings in the integration and interpretation of data. Trait semantics are especially concerned. The aim of this paper is to propose a thesaurus for soil invertebrate trait-based approaches. T-SITA, an Internet platform, is the first initiative to deal with the semantics of traits and ecological preferences for soil invertebrates. It reflects the agreement of a scientific expert community to fix semantic properties (e.g. definition) of approximately 100 traits and ecological preferences. In addition, T-SITA has been successfully linked with a fully operational database of soil invertebrate traits. Such a link enhances data integration and improves the scientific integrity of data.

Dynamic optimization over infinite-time horizon: web-building strategy in an orb-weaving spider as a case study.

Dynamic state-dependent models have been widely developed since 1990s for solving questions in evolutionary ecology. Up to now, these models were mainly run over finite-time horizon. However, for many biological questions an infinite-time horizon perspective could be more appropriate, especially when the end of the modeled period is state- rather than time-dependent. Despite this approach is widely used in the field of economics and operational research, thus far no work has been providing biologists with a general method to solve infinite-time horizon problems. Here we present such a method, through the exhaustive description of an algorithm that we implement to determine the strategy an organism should follow to reach a particular state as fast as possible while limiting mortality risk. To illustrate that method we explored web-building behavior in an orb-weaving spider. How are adult females predicted to build their successive webs to gain energy, grow, and lay their first clutch as fast as possible, without suffering from either predation or starvation? From this example, we first show how an optimal strategy over infinite-time horizon can be processed and selected. Second, we analyse variations of the optimal web-building strategy along with the spider's body weight and predation risk during web building. Our model yields two main predictions: (1) spiders reduce their web size as they are gaining weight due to body-mass-dependent cost of web-building behavior, and (2) this reduction in web size starts at lower weight under higher predation risk.

Body-mass-dependent cost of web-building behavior in an orb weaving spider, Zygiella x-notata.

In numerous spider species, reproductive success of adult females has been shown to be positively correlated with their body mass. We suggest, however, that spiders may incur greater foraging costs as their body mass increases due to the numerous and complex locomotor bouts needed to build an orb-web. Such a body-mass-dependent cost should, in turn, affect the web-building decisions of spiders. In the laboratory, we tested the influence of body mass on energetic expenditure (measured as mass loss) during web-building behavior in Zygiella x-notata. Our results showed (1) that energetic costs associated with web-building were closely related to body mass and to web-building activity, and (2) that as their body mass increased, spiders reduced the amount of silk used per web, while their foraging effort simultaneously increased. This work gives new insights into web-building behavior and energy allocation strategies of weaving spiders.